Okay, just noticed that the magnifying glass is missing in IE and FF outside of the plugin also. So it's not an issue with the plugin.
It looks like Google has eliminated the magnifying glass from their homepage in favor of the Google Search button underneath the search box. Unfortunately, clicking that button does not do anything. It's curious that the I'm feeling lucky button next to it does launch a search, though. One would think that if it's an issue with a changed page neither of those buttons would work.